This invention relates generally to endoscopes and more particularly to electronic endoscopes.
As is known in the art, an endoscope generally includes an elongated hollow tube having a proximal or viewing end and a distal end. An optical path, including a plurality of lenses is disposed in the tube. An image provided to the distal end of the tube is transmitted along the optical path to the proximal end of the tube. The proximal end of the tube and thus the optical path typically terminate in an eye piece or in an objective plane of a microscope.
As is also known, such endoscopes may be used by physicians and others to view anatomical features of internal organs in a body cavity. In such applications, the physician inserts an endoscope into the body cavity of a patient to provide a clear view of an anatomical feature or body organ of the patient. This is especially true in the case of a surgeon who may have the need to see details of the anatomical features upon which a surgical procedure is to be performed.
As is also known, video cameras have taken a greater role in the surgical theater with the advent of lighter, smaller and higher resolution video cameras. Endoscopes may be fitted with such video cameras to allow the physician to view anatomical features of interest on a video monitor. Thus, there exists a trend to terminate the optical path of the endoscope in a video camera which may in turn be coupled to a video monitor.
One problem with such endoscopes however, is that each of the lenses in the optical path generally reflect from each surface thereof up to 1.5 percent (1.5%) of the light incident on each lens surface. When it is necessary or desirable to increase the length of the endoscope, it is necessary to increase the number of lenses in the optical path. An optical path having a large number of lenses provides a relatively large transmission loss to an image which is transmitted along the optical path from the distal end to the proximal end of the endoscope. This is especially true when the lenses are provided having a relatively small diameter. Thus, the image viewed on a video monitor coupled to the proximal end of the endoscope, for example, is relatively dim.
Furthermore, the lenses in the optical path generally reduce the contrast ratio and resolution of the image and also provide chromatic aberrations and geometrical distortions of the image. Moreover, it becomes increasingly more complex and difficult to align each of the lenses included in the optical path. This leads to an increase in the cost of manufacturing the endoscope.